Subscribing to a streaming service through Amazon Channels, as opposed to subscribing directly with the service itself, has certain advantages, such as a single place to manage subscriptions and better integration with the Amazon Fire TV. However, one big disadvantage has been the lack of access to standalone apps, like HBO Now and Showtime Anytime, when subscribing through Amazon Channels. That is starting to change because some services have started including Amazon Channels in their list of service providers that can be used to activate their standalone apps.
Thanks to CordCuttersNews for pointing it out, HBO now gives you the option to select Amazon Channels as your service provider to activate their HBO Now app. I checked and Showtime now also has the option to activate using an Amazon Channels subscription.
This means you can subscribe to these services through Amazon Channels, get all the advantages that come with doing so, and still have access to all the same apps as a direct subscriber would. There’s unfortunately no central list of services that provide this type of additional access, so you’ll have to check for yourself if an Amazon Channel you’re subscribed to, or thinking of subscribing to, allows you to activate their standalone app in this manner.